A vessel or other floating structure such as drilling or service rigs or similar may comprise an underwater space for example as a service space or hoisting shaft for a propeller device or similar system. Such an underwater space comprises a closed or closable space into which an access for the crew is arranged from other parts of the vessel or similar floating structure, and which space is arranged in connection with the bottom or side of the vessel or similar floating structure, whereby the propeller device or similar system can be hoisted from its operation position up to the service/storage position in the service space and correspondingly lowered from the service space down to the operation position.
The underwater space is equipped with at least one watertight closing device, such as a hatch or other removable construction part, arranged in the bottom or side of the vessel or similar floating structure which when open form a direct connection from the underwater space into water in order to lower the propeller device from the service space into water to its operation position, i.e. its operation mode, and correspondingly to hoist from water inside the service space into service/storage position, i.e. service/storage mode, and which when closed forms a watertight space together with the other structures of the underwater space, from which water can be removed after closing the closing devices.
The opening of the underwater space is closed in a watertight manner by a hatch or other removable construction part that is in one or several parts, the construction part being typically attached to the hull structure of the vessel mechanically via bolts or other similar fastening means. When it is desired to open the hatch/hatches or removable construction part for hoisting or lowering the propeller device through the underwater opening, the hatch/hatches or removable construction part hoist up in their guides or turn to the side. The hatch/hatches or other removable construction part is opened/closed via an actuator designed for this purpose, and is kept temporarily locked via for example hydraulic cylinders or other similar actuators, in order to be able to remove or attach the mechanical fastening means such as bolts or similar, used for attaching the hatch or other construction part. The use of such solutions based on hydraulic cylinders as locking devices is problematic since they need operational energy in order to lock and to keep locked. The buoyancy force directed to underwater hatches is significant, thus the pressure directed to the cylinders is high and thereby the amount of operational energy is also significant. Moreover, such actuators are large, heavy and require space.